Question: When did the Cossack Hetmanate cease being a vassal of the Ottoman Empire?
Paraphrase: On what date was the Cossack Hetmanate frei from the  subordination to the Ottoman Empire?
SPARQL (Wikidata): SELECT ?value WHERE { wd:Q212439 p:P31 ?s . ?s ps:P31 wd:Q2560551 . ?s pq:P582 ?value}